arXiv subjects

G Vaitheeswaran

Publications and source records attributed to G Vaitheeswaran.

3 recordsLinked to original sources

arXiv2026

Pressure induced Electronic and Structural Transition in Ba$_2$NiTeO$_6$

This study explores the pressure evolution of the double perovskite Ba$_2$NiTeO$_6$ by employing experimental and computational techniques. For the study of structural and vibrational properties, synchrotron X-ray diffraction (XRD) and micro-Raman spectroscopic experiments at high-pressures were carried out. As a complementary study, DFT simulations of the structural properties as a function of pressure were performed to support and explain the experimental findings. Furthermore, the electronic and magnetic properties as a function of pressure were investigated using DFT. Our study reveals a structural phase transition from a rhombohedral $R\bar{3}m$ to a monoclinic $C2/m$ phase at high pressure, accompanied by a significant increase in bulk modulus. Certain anomalies were observed in Raman mode frequencies at lower pressures of about 1 GPa, indicating changes in the electronic structure with a modification from direct to indirect bandgap in the sample. A minimum in the Raman mode full-width-half-maximum (FWHM) at about 11 GPa, coincides with an increase in ordering in the sample, indicated by a drop in the distortion index of Ni-O$_6$ octahedra as well as a discontinuity in the $c/a$ ratio.

cond-mat.mtrl-sci↗

arXiv2016

Predicted thermoelectric properties of olivine-type Fe2GeCh4 (Ch = S, Se and Te)

We present here the thermoelectric properties of olivine-type Fe2GeCh4 (Ch = S, Se and Te) using the linear augmented plane wave method based on first principles density functional calculations. The calculated transport properties using the semi-local Boltzmann transport equation reveal very high thermopower for both S and Se-based compounds compared to their Te counterparts. The main reason for this high thermopower is the quasi-flat nature of the bands at the valence and conduction band edges. The calculated thermopower of Fe2GeCh4 is in good agreement with the experimental reports at room temperature, with the carrier concentration around 1018-1019cm-3. All the investigated systems show an anisotropic nature in their electrical conductivity, resulting in a value less than the order of 102 along the a-axis compared to the b- and c-axes. Among the studied compounds, Fe2GeS4 and Fe2GeSe4 emerge as promising candidates with good thermoelectric performance.

cond-mat.mtrl-sci↗

arXiv2016

Predicted superconductivity of Ni2VAl and pressure dependence of superconductivity in Ni2NbX (X = Al, Ga and Sn) and Ni2VAl

A first-principles study of the electronic and superconducting properties of the Ni$_2$VAl Heusler compound is presented. The electron-phonon coupling constant of $λ_{ep}$ = 0.68 is obtained, which leads to a superconducting transition temperature of T$_c$ = $\sim$4 $K$ (assuming a Coulomb pseudopotential $μ^*$ = 0.13), which is a relatively high transition temperature for Ni based Heusler alloys. The electronic density of states reveals a significant hybridization between Ni-$eg$ and V-$t_{2g}$ states around the Fermi level. The Fermi surface, consisting of two electron pockets around the X-points of the Brillouin zone, exhibits nesting and leads to a Kohn anomaly of the phonon dispersion relation for the transverse acoustic mode TA2 along the (1,1,0) direction, which is furthermore found to soften with pressure. As a consequence, T$_c$ and $λ_{ep}$ vary non-monotonically under pressure. The calculations are compared to similar calculations performed for the Ni$_2$NbX (X = Al, Ga and Sn) Heusler alloys, which experimentally have been identified as superconductors. The experimental trend in T$_c$ is well reproduced, and reasonable quantitative agreement is obtained. The calculated T$_c$ of Ni$_2$VAl is larger than either calculated and observed T$_c$s of any of the Nb compounds. The Fermi surfaces of Ni$_2$NbAl and Ni$_2$NbGa consist of only a single electron pocket around the X point, however under compression second electron pocket similar to that of Ni2VAl emerges only in Ni2NbAl and the Tc increases non monotonically in all the compounds. Fermi surface nesting and associated Kohn anomalies are a common feature of all four compounds, albeit weakest in Ni$_2$VAl.

cond-mat.supr-con↗